George Zimmerman’s acquittal Saturday night on all charges in the killing of a black teenager, Trayvon Martin, sparked deep emotional reactions across the country Sunday, resurrecting an intense national debate about the role of race and racism in American life.

President Obama declared Martin’s killing an American tragedy but called for calm.

From church pews to street corners to the sprawling social-media universe, Americans expressed outrage, disgust and, in some cases, relief at the verdict. Rallies and vigils were held in Washington, San Francisco, Chicago, New York and Los Angeles as well as in Sanford, Fla., where the killing and the trial took place. Others were scheduled in Boston, Detroit and Baltimore.

“I grew up in Georgia, and what happened to Trayvon would be the norm for any black man in Georgia,” said James Ealey, 73, recalling an earlier, more segregated nation. “That was the way it was. We are going backwards. We are not in a post-racial America just because of Barack Obama,” he said after Sunday services at Metropolitan African Methodist Episcopal Church in Washington.

The White House issued a statement in which Obama characterized Martin’s death as “a tragedy . . . not just for his family . . . but for America.” The president acknowledged that “passions may be running ever higher” in the wake of the verdict but urged citizens to remember that a jury had spoken.

“I now ask every American to respect the call for calm reflection from two parents who lost their young son,” Obama said. “And as we do, we should ask ourselves if we’re doing all we can to widen the circle of compassion and understanding in our own communities . . . if we’re doing all we can to stem the tide of gun violence that claims too many lives across this country on a daily basis. . . . That’s the way to honor Trayvon Martin.”

The verdict did little to close the stark divisions the case opened up among Americans along the jagged fissures of race and personal safety — starting when Martin was shot about 18 months ago.

A Zimmerman attorney argued throughout the case that race had little bearing on the initial confrontation or the outcome. But the case has played out against a racially charged backdrop since Zimmerman followed the unarmed Martin as he walked through his central Florida neighborhood and later said a confrontation led him to shoot Martin in self-defense.

As one side sees it, a racially biased criminal justice system was slow to charge Zimmerman and quick to believe a white man’s version of events. The other side sees in Zimmerman a law-abiding citizen who tried to protect his neighborhood and properly claimed his right to carry a weapon in self-defense.

Protesters across the country decried what they called the injustice of Zimmerman’s acquittal. They insisted that something must change in a court system and body of law that would allow an armed and self-appointed neighborhood watchman to pursue a black teenager, based on the suspicion that he was up to no good, and kill him.

A group called the Coalition for Justice for Trayvon hosted a rally Sunday afternoon at the Seminole County courthouse, where a jury of six women acquitted Zimmerman of second-degree murder. In Washington, critics of the verdict were pumping fists and chanting along the U Street corridor early Sunday morning. Among the placards they carried were these two messages: “Stop criminalizing black men” and “Only White Life is Protected in America.”

The NAACP began circulating a petition late Saturday asking Attorney General Eric H. Holder Jr. to take action in the case as the group held its annual conference in Orlando.

“It is time for the Department of Justice to act,” the petition says. “The most fundamental of civil rights — the right to life — was violated the night George Zimmerman stalked and then took the life of Trayvon Martin.”

During a vigil Sunday night at Howard University, students, community members and alumni honored Martin with a moment of silence and the hymn “Lift Ev’ry Voice and Sing.” Then Taylor Davis, a Howard student who is president of the school’s NAACP chapter, delivered a rousing address that had the crowd shouting in affirmation.

“We will honor the voice of the jury, but we will put ourselves in a position where they will honor our voices as well. Make noise,” she said. She urged her listeners to sign the petition and to register to vote so that they can cast ballots against lawmakers who support legislation like the “stand your ground” law that protected Zimmerman.

Although some people criticized the verdict, many argued that state investigators should have never prosecuted Zimmerman, because there was simply not enough evidence to prove who was the aggressor. Even legal analysts who said they strongly suspected that Martin was an innocent victim agreed that evidence proving so beyond a reasonable doubt — the standard that must be met for a guilty verdict — did not exist in this case.

Ultimately, there were no living witnesses other than Zimmerman.

Zimmerman said Martin punched him and threw him to the ground. A few neighbors testified that they heard yelps and saw an altercation but not who was doing the harm. A friend of Martin’s said he had called her on her cellphone minutes before his death, complaining that he was afraid of a “creepy-ass cracker” following him.

Attorneys for Zimmerman said at a post-verdict news conference that they were ecstatic at the decision and praised the jurors, saying they weighed the evidence carefully. But defense attorney Mark O’Mara complained that some in the public and the media turned Zimmerman into a civil rights cause — and a monster.

“If only those who decided to condemn Mr. Zimmerman as quickly and as viciously as they did would have taken just a little bit of time to find out who it was that they were condemning, it would never have happened,” O’Mara said.

Added another defense attorney, Don West: “I think the prosecution of George Zimmerman was disgraceful. . . . It makes me sad, too, that it took this long, under these circumstances, to finally get justice.”

The Justice Department opened a civil rights investigation of Martin’s death shortly after his shooting. A department spokesman said Sunday that the investigation remains open and that officials are looking at whether there is enough evidence to pursue a civil rights case.

But for many Americans furious with the jury’s decision, Sunday was a day to look to their religious faith for comfort and understanding.

Among them was Martin’s mother, Sybrina Fulton, who tweeted about her deep faith and quoted Proverbs 3:5-6: “Trust in the LORD with all your heart and lean not on your own understanding; in all your ways submit to him, and he will make your paths straight.”

She also tweeted: “Lord during my darkest hour I lean on you. You are all that I have. At the end of the day, GOD is still in control. Thank you all for your prayers and support. I will love you forever Trayvon!!! In the name of Jesus!!!”

Martin’s parents and relatives were “in church this morning, praying and turning to God, a higher authority, to make sense of it all,” family attorney Benjamin Crump said Sunday on ABC’s “This Week With George Stephanopoulos.” The family cannot believe the verdict, Crump said.

They don’t fault the prosecutors, he said, but they are trying to make sense of the jury’s decision while continuing to mourn the 17-year-old’s death. Family members are trying to decide what to do next and will look into filing a civil lawsuit. They have set up a foundation in Martin’s memory and pledge to fight gun violence.

In sermons Sunday, many pastors mentioned the verdict and the pain it had caused their flocks. At some churches, members wore hooded sweatshirts in Martin’s honor to bring attention to racial stereotypes about young black men who wear such attire.

But Sunday was a day of celebration for supporters of Zimmerman, who believed he had properly defended himself from a threat and should never have been prosecuted.

His brother, Robert Zimmerman Jr., tweeted early in the day: “Message from Dad: ‘Our whole family is relieved’. Today . . . I’m proud to be an American. God Bless America! Thank you for your prayers!”

Manuel Roig-Franza in Sanford, Fla., and Hamil R. Harris, Sari Horwitz and Julie Zauzmer in Washington contributed to this report.

Carol Leonnig covers federal agencies with a focus on government accountability.

Jenna Johnson writes about Maryland politics, including the General Assembly, the administration of Gov. Martin O'Malley and the 2014 election.

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